The present invention pertains to filtering, and more particularly to a filter for filtering solid particles from liquids, and which is further provided with a system for washing down the filter periodically with the use of automated sensors and controls.
In many industrial processes it is necessary to handle finely divided particulate materials. It is often necessary to be able to clarify and filter solid particles from liquids, for example in cooling tower systems, ozone based systems that use chemical treatment, and ozone treatment or a combination.
There are many filtering devices designed to remove particulate material from such liquids. For example, sand filters are used but they are impractical due to the long down time required to clean the filters and due the continued absorption of ozone because of incomplete washing of the sand in sand filters.
The same problem is also encountered with conventional bag filters and the like. The down time for cleaning such filters is excessive, expensive and laborious, and in addition, such filters do not provide any means for determining when filter cleaning is required. Such systems also generally use a backwash system for cleaning which may use previously chemically or ozone treated water for cleaning the filter.
It is a principal object of the present invention to provide a filtering apparatus for removing solid particles from a liquid which incorporates apparatus for automatically detecting when filter cleaning is required, and also automatically initiates and concludes the filter cleaning process without the required attendance of maintenance personnel.
The filtering apparatus of the present invention for removing solid particles from liquid includes a pressure-tight cylindrical housing with a filter assembly coaxially mounted in the housing. A cylindrical filtering surface, such as a fabric bag filter, is provided on the filter assembly and the filter assembly has an internal liquid passage for downward egress or draining of filtered liquid.
A liquid inlet is provided at the upper end of the housing and is preferably made tangential to the housing for imparting swirling cyclonic movement of the liquid to be filtered within the cylindrical housing.
A liquid outlet is provided at the bottom of the filter assembly for draining filtered liquid from the filter assembly internal passage through a bottom portion of the housing. A drain is also provided in the lower end of the housing for draining off accumulated solids from the housing exteriorly of the filter assembly.
A wash-down apparatus is provided in the upper end of the housing for directing a wash liquid, such as water, under pressure against the filtering surface for washing the filtering surface down. In addition, a pressure differential sensor control is connected for sensing pressure differential between the interior of the housing and the outlet passage. This pressure differential sensor control is operable for closing the inlet and outlet passages of the filtering apparatus, opening the bottom drain in the housing and for also initiating the wash-down apparatus when a predetermined pressure differential is attained. The wash-down process is timed and when completed the process is automatically reversed to continue normal filtering operation of the filtering apparatus for filtering liquids.
An additional feature of the filtering apparatus of the present invention is the inclusion of a vacuum break valve connected for providing exterior air to the interior of the housing when the vacuum break valve is opened. The afore described pressure differential sensor is also operable to open this vacuum break valve after first closing the inlet and outlet passages for the filtering apparatus.
The opening of this vacuum break valve breaks the vacuum normally provided within the filter housing and permits a large ingress of exterior air of higher pressure. This causes the filter fabric bag, which is supported on a perforated cylinder, to literally jump or pulse off of the supporting perforated cylindrical surface, which causes the solid particles entrapped in the filter fabric to be loosened and more easily and readily washed down by the wash-down apparatus.
To assist in this vacuum break function, the filter assembly preferably includes a standoff support disposed on the exterior of the perforated vertical cylinder whereby the filter bag fabric is disposed over the standoff support and the perforated cylinder on which it is mounted such that at least portions of the filter fabric are prevented from contacting the perforated cylinder. When the vacuum break is initiated this causes the pulsing of the filter fabric to be greatly exaggerated or accentuated whereby the initial loosening of solid particles entrapped in the filter fabric is also accentuated for better effect. The standoff support may be constructed of, or include, a series of heavy debris expulsion rods that are annularly spaced about the exterior of the perforated cylinder with their axis aligned in parallel with the axis of the cylinder. These rods also further serve to break up larger particles as they rotate around these rods.
The timer mechanism is connected for timing out the wash-down cycle and disengages the wash-down apparatus and closes the drain and the vacuum break valves and opens the inlet and outlet valves for the filtering apparatus to reestablish normal water filtering after a predetermined wash-down time.
The filtering apparatus of the present invention is also be provided with an automatic air vent valve connected to the inlet for venting entrapped air in the inlet line, so that the filter vessel can vent off entrapped air before going back on line.